Electric heater unit

ABSTRACT

The system includes a plurality of elongated bars extending in spaced generally parallel relation one with the other with each bar defining a central fluid passage. Pairs of elongated fins project from each of the four sides of the bar. The bars are fluid connected at both top and bottom to form a fluid circulation system. A heating element is applied to at least one of the bars along an external surface thereof to heat the fluid within the passages. A pair of covers are provided between each adjacent pair of bars and define with such adjacent bars an air duct between adjacent fluid passages. The heating element is under the control of a thermostat and a heat responsive control switch, the latter serving to cycle the heating element for on off operation until the room temperature obtains the thermostatic setting. The bars and covers are provided in decorative and esthetically pleasing spacial forms.

[ Dec. 3, 1974 1 ELECTRIC HEATER UNIT [76] Inventors; Roger P. Michaud, 5 McKiney Rd.,

' Falmouth Foreside, Maine 04105;

Jacques Cordes, 30-32 Rue DAnjov, Versailles, France 78 22 Filed: Jan. 9, 1973 21 Appl. No.: 322,116

[52] US. Cl 219/365, 165/129, 219/341,

219/364, 219/378, 237/16, 237/79 [51] Int. Cl F24h 9/00, H05b 1/00 [58] Field of Search 219/341, 365, 378;

[56] References Cited UNITED STATES PATENTS France 219/341 1,037,103 8/1958 Germany 165/129 711,314 9/1949 Germany 219/341 11,531 8/1905 Great Britain... .1 165/130 980.850 1/1951 France 219/341 Primary ExaminerA. Bartis v Attorney, Agent, or Firm-LeBlanc & Shur [57] ABSTRACT The system includes a plurality of elongated bars extending in spaced generally parallel relation one with the other with each bar defining a central fluid passage. Pairs of elongated fins project from each of the four sides of the bar. The bars are fluid connected at both top and bottom to form a fluid circulation system. A heating element is applied to at least one of the bars along an external surface thereof to heat the fluid within the passages. A pair of covers are provided be- 11/1891 Goodflch 237/79 X tween each ad acent pan of bars and define with such 863,211 8/1907 Paul 2.19/341 UX U74626 3/1916 shipp 237/79 X ad acent bars an air duct between ad acent fluid pas- 1,397,097 11/1921 Harrison.... ..3... 165/129 sages- The heating element is under the Control of a 2,477,734 8/1949 Gehrke g g 3 5 x thermostat and a heat responsive control switch, the 2,917,617 12/1959 Gruebel 219/341 X latter serving to cycle the heating element for on off ,2 H1969 Grossinger /3 1 operation until the room temperature obtains the ther- 3,538,307 11/1970 Birdwell 237/16 X mostatic setting The bars and covers are provided in FOREIGN PATENTS OR APPLICATIONS decorative and esthetically pleasing spacial forms.

809,771 4/1969 Canada 219/341 15 Claims, 12 Drawing Figures PATENTE DEB 3mm SHEET 2 OF 3 PATENIELUEB 31914 swam 30F 5 HEATER UNIT THERMOSTAT HEATER THERMOSTAT ROOM BLOWER) HGIZ 1 ELECTRIC HEATER UNIT DESCRIPTION OF THE INVENTION The present invention relates to a heating system and particularly relates to an electrical heating system of improved efficiency and wherein the heating elements serve as well as decorative and esthetically pleasing elements of a room or divider therefor.

A wide variety of heating systems have been proposed and constructed in the past. One such system is disclosed in French Patent No. 2,044,549. In that system, thereis provided a plurality of bars each having a central passage and a pair of fins coextensive in length with the bar projecting from each of the four sides thereof. The central passages of each bar are interconnected with the central passages of adjacent bars through generally H-shaped connections disposed at opposite ends of and between each next adjacent pair of bars. Fluid is supplied to the central passages of these bars from a central heating system, for example, a boiler located in the basement of a building. The bars and fins carried thereby form radiating surfaces for heating the surrounding environment. Also, the-fins of the bars are provided with laterally projecting beads along their outer edges to further enhance the esthetically pleasing appearance of the bars and fins. While this heating system has proved satisfactory, it is connected to the central heating system of an entire building. This restricts its use in buildings to locations adjacent the built-in heating and return pipes. As such, that system is not readily disposed in esthetically desirable locations or locations of optimum heating efficiency without extensive and expensive modification to the plumbing of the building. Consequently, the bars of that system cannot as frequently as desirable be conveniently located for optimum heating efficiency or readily serve as a functional part of a room, for example, as a room divider. More importantly, the heating tion, mode of operation, use and efficiency in comparison with such prior systems. Particularly, the present invention includes, as in the French Patent No. 2,044,549, a plurality of bars each having a central fluid passage. The bars are arranged in spaced side-byside generally parallel relation one to the other. Each bar has a pair of fins extending from each of the four sides thereof and extending generally coextensively therewith, each fin having a laterally outwardly directed bead along its outer edge. Connections are provided between next adjacent bars at their opposite ends, the connections having fluid passages whereby the passages in the bars are interconnected one with the other. In accordance with the present invention, an electric heating element is disposed along the side face of one of the bars to heat the fluid contained within the closed passages. The passages are also closed at each of the opposite ends of the bars by flexible elements .which are laterally expanded into sealing engagement along the interior walls of the bars. Thus, with each of the bars closed at its opposite ends, a closed fluid circulating system is provided. The heating element is under the control of a room thermostat and it will be appreciated that the heating element heats the fluid contained within the bars whereby the heat is transferred to the fins and radiated to the surrounding environment.

Another form of the present invention utilizes the structure disclosed above and, in addition, provides covers between next adjacent bars to form air ducts substantially coextensive in length with the bars. Particularly, the covers are generally channel-shaped and have a continuous inwardly directed bead along the outer edges of their legs. To apply the covers, the beads on the legs of the covers are snapped past the beads formed along the laterally aligned pair of fins of the next adjacent bars. Thus, it will be appreciated that with two covers applied on opposite sides-of the space between adjacent bars, there is provided an air duct defined by the side fins and central wall portions of the adjacent bars and the opposed channel-shaped ducts. The covers are, of course, applied between a plurality of adjacent'bars whereby a plurality of air ducts are interspaced with the fluid ducts. The bases of the covers are preferably arcuate and complement the esthetically pleasing appearance of the bars.

In one form of this aspect of the present invention, the ducts are open at opposite ends. in a further form of this aspect of the present invention, a blower unit is provided adjacent the lower ends of the bars in comm unication with the lower ends of the air ducts. The blower unit has an intake duct along one side thereof and a rotary blower for blowing air upwardly through the air ducts. The upper surface'of the blower housing is configured in accordance with the outline of the bars and ducts thereby to direct substantially all of the air into the ducts and also to provide an esthetically pleasing appearance. Thus, in this embodiment of the invention, the surrounding environment is heated both by radiation from the duct covers and bars as well as by the heated air circulated by the blower through the air ducts.

A preferred form of, the present invention provides a heat responsive control switch which, in conjunction with the thermostat, controls the on-off operation of the heating element in a manner to achieve optimum efficiency in both heating the environment and in the the heater. When the thermostat is set to the desired temperature and the temperature of the surrounding environment is lower than the desired temperature, the thermostat completes 'the circuit to the heating element to heat the fluid in the passage and indirectly the air in the ducts. After the fluid and metal forming the ducts reaches a predetermined temperature, the control switch turns off the heating element and maintains the element off until the temperature of the fluid and metal obtains s specified lower temperature. When this occurs, the control switch turns the heating elementon until the predetermined fluid and metal temperature is obtained. The heating element is thus cycled between on and off conditions during the time that heat is being called for by the thermostat. It will be appreciated that during the time the heating element is being cycled, that is, periodically turned on and off, heat is provided tion optimizes the use of the heat suppliedby the heating element to the system while minimizing the electrical energy necessary torun the heating element. In

short, the BTUs per kilowatt hours is optimized. Also,

it will be appreciated that circulating pumps for the fluid are not necessary or provided. The fluid, circulates through the closed system by a thermosiphon effect whereby the heated fluid is distributed throughout the bars.

A further feature of the present invention resides in the use of a pressure relief valve. This relief valve constitutes 'one of the closure members at the ends of the bars. Each closure member includes a flexible member disposed between two rigid members which are connected one to the other by a screw extending through the flexible member. By torquing a nut on the end of the screw, the flexible member is axially compressed FIG. 3'is'an enlarged cross-sectional viewof the heating element disclosed in FIG; L and taken generally about on line 3'3 in FIG.- 1;. x "FIG.,4 is an enlarged fragmentary vertical crosssectional view of the upper ends of the unit and taken generally abouton line4-4 in FIG. 3; i

' FIG. 5 is an enlarged cross-sectional view thereof taken about on line 55 inFIG. 1;"

FIG. 6 is an enlarged cross-sectional view of one of the heating bars illustrated in FIG. 1;

FIG. 7 is anenlarged cross-sectional view of the air duct forming cover forming apart of the heating unit illustrated in FIGLI; L

FIG. 8 is a perspective view of a fluid connection for joining the adjacent bars;

FIG. 9 is a cross-sectional view taken about on line 9--9 in FIG. 1' with parts broken out and illustrating the heating element and control switch;

FIGS. 10 and 11 are schematic illustrations of three and four bar heating systems respectively of the present invention and illustrating the fluidv and air paths of the heating mediums; and i FIG. 12 is a schematic illustration'of an electrical circuit for use in the present heating system.

Referring now to the drawings, particularly to FIG. 1, there is illustrated a heating system constructed in accordaricewith the present invention and comprised of pressure, the seal is displaced beyond the vent hole to release the pressure in the closed fluid system.

Accordingly,it is aprimary object of the present invention to provide a novel and improved heating system which obtains high efficiencies in the transfer of heat to the surrounding environment and in the utilization of the electrical energy required to produce the heat.

i It is another object of the present invention to provide a novel and improved heating unit which not only provides optimum efflciencies in heat transfer and utilization of electrical energy but which is also esthetically pleasing in appearance and can be used functionally-as portions ofa room, for example a room divider.

Itis still another object of the present invention to provide a novel and improved heating system including a closed flui'd'circuit distributing heated fluid to the radiating finsbf the heating unit in combination with air ducts for efficientl ytransferring the heated air from the heating system. i Y I It is a further object of the present invention toprovide a novel and improved heating system including an electrical heating element which is cycled-between on and off positions during the time that heat is called for by a thermostat whereby maximum efficiency in the conversion of electrical energy to heat is obtained.

It is still a further object of the present invention to provide a novel and improved'heating system having the foregoing characteristics and including a pressure relief valve for providing, effective pressure relief at a predetermined internal pressure.

These and further objects and'advantages of the 'present invention will become more apparent upon reference to the following specification, appended claims and drawings wherein: I l

FIG. I is a perspective view of a heating unit constructed in accordance with the present invention and with parts broken outfor' ease of illustration;

FIG. 2 is a perspective view of a blower unit for theheating element of FIG. I;

a a heating unit generally designated 10. Unit l0 includes a plurality of bars generally designated 'l2 arranged in side-by-side generally parallel relation one to the other. Each bar 12 is comprised of an elongated metal, preferably aluminum, extrusion having a central rectilinear body portion 14 defining a fluid passage 16 therethrough andwhich passage is generally square in cross section. A pair of fins 18 project from each of the four sides of the rectilinear body portion 14, the fins being generally coextensive with the length of the bar and coplanar with a pair of the side walls of body portion 14. That iseach'fln in effect constitutes a continuation of a wall of the body portion 14 defining a passage 16. The outer edge of eaehfln 18 carries a small normally directed flange 2i) oneedge of which also carries an inwardly directed bead 2 2iFlanges 20 and'beads 22 are coextensivein length with the associated fin :18. It will be appreciated that each bead .22 forms agroove 24 with the corresponding body portion of the associated fin for purposes which will become clear from the ensuing description. The bars are coated or painted to any desired color and'it will be appreciated that the bars per se provide an esthetically pleasing appearance.

Adjacent bars are interconnected one with'the other adjacent each of their opposite ends by a connection generally designated -26 and depicted particularly in. FIG. 8. Connection 26 is comprised of a generally I-I- shaped body 28 having a central portion 30 which defines a passage 32 between opposite sides of the connection. At least one set of opposed legs 34 of connection 26 has openings 36 for receiving bolts to secure the connections 26 to the adjacent bars 12. Each bar has a pair of laterally registering side openings 38 which.

when the connection isinserted between the side fins I8as illustrated in FIG. 3, register with the passage 32 of connection 26 whereby fluid communication be- .tween the central passages 16 of adjacent bars is estab- 42 formed along the outer sides of connection 26. The p diameter of the opening through the square washer 40 is smaller than the diameter of passage 32. Thus, when the connection 26 is secured to the bars, the washers line of the blocks 46, 47 and the flexible pads. 48 is slightly smaller than the rectilinear outline of the walls defining passage 16. A screw 49 fixed to the inner block 46 extends through a central opening in the flexible pads 48 and through a central opening in the outer block 47. A nut 50 is threaded onto screw 49. When the seals 44 are inserted into the ends of the bars, the nuts are torqued to displace blocks 46 and 47 toward one another and thereby to axially compress and laterally expand the flexible elements against the inner walls of body portion 14 to provide a fluid seal.

One of these seals, however, serves as a pressure relief valve, for example seal 51. This seal 51 is similar in all respects to the seals 44 except that its nut 52. is torqued to a lesser extent. This permits it to form an effective seal when theheating unit is operated normally but permits it to slip at a predetermined internal pressure. A vent'opening 54 is provided adjacent the end of the barcontaining the pressure relief valve. Thus, when seal 51 slips past the vent hole 54, the pressure in the closed system will be relieved through the opening 62. Note that the vent, opening 62 is formed along a side wall of the bar whereby pressure relief is directed against an adjacent bar and not outwardly into the surrounding environment. I

Referring now to FIG. 5, electrical heating unit 60- is applied along the wall of body portion 14 between the pair of side fins 18. Particularly, a strip type'elec trical heating element is suitably secured, for example by screws to the wall whereby the heating elementheats the fluid in thepassage 16. Such heating unit may be model SNH 17 produced by Bray Chromalox, Leeds 2, England. The heater is asurface type heater and heats the metal of the wall which in part defines thefluid passage whereby the fluid in the passage is heated.

It will be appreciated that with the closed fluid circulating system, the fluid circulates within the passages without aid of pumps or the like. The heat carried by the fluid is transferred through the metal walls to the fins and radiated to the surrounding environment. Any suitable type of fluid can be utilized, for example a percent by volume ethylene gylcol aqueous solution.

In another embodiment of this invention, heat is also circulated to the surrounding environment by air currents. To accomplish this, the spaces between each pair of adjacent bars are closed laterally by covers 70 to form air ducts 71 extending generally parallel to the direction of the fluid ducts. Particularly, each cover 70 is comprised of a generally channel-shaped metal member, preferably an aluminum extrusion, having a slightly arcuate base 72 and a pair of legs 74. The edges of the legs have inturned flanges or beads 76. To apply the elongated covers to the adjoining bars, the legs 74 and flanges 76 carried thereby are snapped pass the beads 22 along the opposed side fins 18 into the grooves 24. That is, the covers 70 are snap fitted to the side fins 18. It will be appreciated that a pair of such covers 70 are disposed between each adjacent pairof bars and thereby define with the bars a plurality of verticallyextending air ducts.

Adjacent the bottom portion of the heating unit,

there is provided a blower unit generally indicated 80 and which comprises a housing 82 having bottom, side, end and upper walls. One side wall is provided with a screened opening 84 and a rotary blower generally indicated 86 is located within the housing to draw air from the surrounding environment through opening 84 into housing 82. The end walls of the blower unit 60 are provided with T-shaped grooves 88. To install the blower unit, the side fins of a pair of bars are received within the Tshaped groove 88. Bars directly above the blower unit 80 are cut short such that the shortened bars terminate adjacent the top of the blower unit. The upper face of the blower unit is cut to the profile indicated at 89 in FIG. 2 and which corresponds in profile to the profile of the duct covers 70 and the front and rear walls of the body portions 14 of the bars 12. It will be appreciated that the shortened bars above the blower unit 80 are interconnected by use of connectionssimilarly as previously described. The cutout upper surface of the blower unit is thus necessary to'insure delivery of air from the blower into the ducts formed by the covers and the adjacent bars.

Consequently, when the heating element is actuated to heat the fluid in theducts, the fluid, in turn, heats the air in the ducts through the walls of the bars therebetween. Also, the air within the ducts is circulated upwardly by the blower unit 60 whereby a circulation of heated air within the'environment surrounding the heater'is provided. s

In a preferred embodiment of the present invention, a heat-responsivecontrol switch or heater unit thermostat 90 is also connected to the bars. Referring to FIG. 12, the switch 90 is electrically connected with the room thermostat T, blower 86, and heating-element 60. The room thermostat senses the temperature of the ambient airin the area heated by the heater unit. The switch 90 serves to cycle the heating'element during the time that heatis required or called for by the thermostat T such that the heating element is on part of the time and off the remainder of the time in each cycle. That is, "heater unit thermostat 90 is responsive to the temperature of theheater unitfor periodically activating and deactivating the-heating element 60 while heat is called for by the thermostat T. For example, when the metal surfaces in contact with switch 90 obtain a predetermined temperature, switch 90 opens'thereby opening the circuit to the heating element 60. When the heat is transferred by the fluid in the fluid passages to the bars and to the air ducts therebetween and eventually to the surrounding environment to the extent that the temperature of the metal contiguous to switch 90 drops below a predetermined temperature, switch 90 closes completing the electrical circuit and thereby actuating the heating element 60. The heating element thus operates periodically whenever heat is called for by the thermostat and this conserves the electrical energy. It has been found that this optimizes the BTUs per kilowatt hours consumed. In short, greater efficiency-in heating per electrical energy consumed is obtained. It will be appreciated that even while the heating element is off, heat is still being provided to the surrounding environment due to the circulation of the fluid in the passages of the bars and the circulation of the air through I the air ducts between the bars and within the covers This cyclic action of the heating element continues until the temperature of the surrounding environment obtainsthe predetermined temperature set at thermostat T and at which time the thermostat opens the circuit. The heating element -is thus turned off under the control of the thermostat. While the heating element is thermostatically turned off, the control switch 90' will I close once the temperature of the metal adjacent the switch drops below the predetermined temperature but will not actuate the heating element since the thermotemperature set at the thermostat. The control switch 90 may be thetype manufactured by-Fenwal, Incorporated, Ashland, Mass., Model No. 30000-0 sold under the tradename Thermoswitch. v

R'eferringnow to FIG. the fluid and air circulating patterns for a threefbar heating unit are schematically illustrated. Ina three bar unit, the heating element 60 is applied on one side of the central bar 12 and the control switch 90 is applied below the heating element 60. The heated fluid flows upwardly by means of a titer-- mosiphon effect throughthe central bar and divides for passage through the connections 30 to the outermost bars. The fluid flows'downwardly through the outermost bars and returns to the centralbars through the lower most connections 30. Simultaneously, the air in the air ducts 71 flows upwardly between the bars. The fluid and air circul'ating patterns are indicated by the solid and-dashed lines respectively with the arrows indicating the direction of flow. a 7

Referring now to FIG. 1 1, the fluid and air circulating patterns for afourbar heating unit are illustrated. In this form, heating element 60 are applied along the sides of the innermost pair of bars 12 and a control switch 90 is applied 'along' the sides of one of the innermost pairs of bars 12.The fluid heated in the innermost pairs of bars flows upwardly as indicated by the full lines and arrows and communicates with the outermost bars through the cross connections 30 at the upper ends ofthe unit. The fluid then moves downwardly through theoutermost bars and returns to the innermost 'bars through the cross connections 30 at the lower ends of these units. While all of the bars lie in fluid communication one with the'oth'er, the heating unit illustrated in FIG. 11 forms essentially a pairof closed circulating systems. As described with respect to FIG. 10,. the air flows into the bottom portions of the air ducts 71 between the bars and upwardly as indi-.-

cated by the dashed lines and arrows through the opened upper ends of the bars.

As will be recalled, and in both FIGS. 10 and ll, the fluid in the bars continues to flow and the air continues to circulate as illustrated by the solid and dashed lines respectively during the time that the heating element is being cycled. That is, when the thermostat calls for heat, the heating element is cycled between on and off conditions by the control switch 90 (both heating elements in FIG. 11 being under the control switch) whereby such circulation patterns continue notwith standing'the fact that the heating element is off for a limited period of time.

v Referring now to FIG..12 which is a schematic illustration of the electrical circuit for the-heating unit hereof, there is illustrated a sourceof electrical energy S connected in series with the thermostat T, more particularly the switch operated by the thermostat T. The motor for the blower unit 80 is connected across the thermostat and electrical energy source and the heating element 16 andcontrol switch90 are connected in series one with the other and in'parallel with the blower unit motor across the thermostat T and electrical energy source S. In this manner, it will be appreciated that any time the thermostat is closed to actuate the heating elements 60, the blower unit 80 is activated. When the control switch 90 opens. during the cyclic action of the heating element previously described, it opens the circuit to the heating element 60 while the blower unit 80 is maintained activated since the switch of thermostat 'T remains closed. When the temperature of the surroundingenvironment obtains the setting of the thermostat, the thermostat switch opens to de-energize the blower unit motor 80. and the heating element 60.

tains a temperature of .l40F., the control switch opens the circuit to the heating element deactivating the latter. When the surface temperature of the barcools to about 130F., the control switch closes'the circuit to the heatingelement and reactivates the same. An average cycle. lasts about 10 minutes with the heating element on for'approximat ely 3 minutes and 35 seconds and off for 6 minutes and 25 seconds. By cycling the heating element in this manner, electrical-energy provided the heating element is conserved and the efficiency of the entire heating system is optimized.

It will thus be appreciated that the objects of the present invention are fully accomplished in the foregoing described embodiments of the present invention in .that there is provided a heating unit having vastly improved efficiency in the conversion of electrical energy into heat. Moreover, the present improved heating unit is provided such that it may form afunctional part of the room, for example, a room di.vide r,,and also is es thetically pleasing in appearance. Furthermore, it will be appreciated that the heatingunit hereof is not dependent upon the built-in heating system of a building but rather constitutes in one form hereof an independent closed circulating heating system which can be disposed as desired to blend in and enhance the esthetic qualities of the surrounding environment as well as to heat the same. 7

The invention may be embodied inother specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come" within the meaning and range of equivalency of the claims are therefore intendedto be embraced therein.

What is'claimed and desired tobe secured by United States Letters Patent is: v v v l-.-A heater unit comprising a plurality of elongated bars disposed in'spaced generallyparallel side by side:

, 9- ing said bars adjacent opposite ends thereof to permit circulation of fluid from one bar to another,-each of said bars having a pair of fins projecting from each of the front, rear and side faces thereof, said fins being substantially coextensive in length with said bars, means carried by said heater unit for heating the fluid adapted to circulate through said bars, a pair of elongated covers disposed between each next adjacent pair of bars and respectively adjacent the front and rear sides thereof, means for connecting said covers to said next adjacent bars whereby said pairs of covers and adjacent bars define air ducts for circulating air heated by the fluid adapted to circulate through said passages, each of said covers being generally channel-shaped in cross section, and means carried by the legs of each channel-shaped cover for securing the same to a pair of opposed side fins of the next adjacent bars.

2. A heater unit according to claim 1 wherein the passages in the bars define a closed system for circulating fluid.

3. A heater unit according to claim 2 wherein said heating means includes a heating element secured along'one side of one of said bars.

4. The heater unit according to claim 1 wherein said opposite side fins have beads projecting along their edges in a direction away from one another and defining grooves therewith, the legs of said covers having beads along their edges projecting toward one another, said legs being flexible to permit the beads carried thereby to snap past the beads carried by said fins for engagement within said grooves.

5. A heater unit according to claim 1 including means for sealing the ends of the passages in said bars and including a flexible element in the endsof said passages, means for compressing said flexible element in a direction generally parallel to the axis of said bar to laterally enlarge said element into sealing engagement against the walls of said bar defining said passage to thereby seal the latter.

6. A heater unit according to claim 1 including means for closing the ends of said bars thereby providing a closed circulation system, said heating means including an electrical heating element, a thermostat connected to said heating element for activating'said heating element in response to the sensing-of a specified ambient air temperature, and control means for periodically activating and deactivating said heatingelement during the time said heating element is activated by said thermostat.

7. A heater unit according to claim 6 wherein said control means includes temperature responsive means responsive to heater unit temperaturev for activating said heating element in response to sensing a first predetermined temperature and for deactivating said heating element in response to sensing a second predetermined temperature higher than said first predetermined temperature. 7

8. A heater unit according to claim 7 wherein said predetermined first and second temperatures constitute the surface temperatures of one of said bars adjacent said control means.

9. A heater unit according to claim l including means carried thereby for circulating air through said ducts.

10. A heater unit according to claim 1 including a heat exchange fluid in the passages of said bars and in said interconnecting means.

11. A heater unit comprising a plurality of elongated bars disposed in spaced generally parallel side by side relation one to the other with each bar defining a passage for containing a heating fluid, each of said bars having a pair of fins projecting from each of the front, rear and side faces thereof, said fins being substantially coextensive in length with said bars, means interconnecting said bars adjacent opposite ends thereof to permit circulation of a fluid from one bar to another, means for closing the ends of said bars thereby providing a closed path for circulating fluid through the unit, means carried by said heater unit for heating the fluid adapted to circulate through said bars including an electrical heating element, a thermostat connected to said heating element for activating said heating element in response to sensing a specified ambient air temperature, control means including temperature responsive means responsive to heater unit temperature for periodically activating and deactivating said heating element during the time said heating element is activated by said thermostat, said temperature responsive means being responsive to sensing a first predetermined heater unit temperature for activating said heating element and responsive to sensing a second predetermined heater unit temperature higher than said first predetermined temperature for deactivating said heating element whereby said heating element is operated cyclically during the time the heating element is activated by said thermostat, a pair of elongated covers disposed between each next adjacent pair of said bars and respectively adjacent the front and rear sides thereof, means for connecting said covers to said next adjacent bars whereby said pair of covers and next adjacent bars define air ducts for circulating air heated by the fluid adapted to circulate through said passages, each of said covers being generally channel-shaped in cross section, and means carried by the legs of said channel-shaped covers for securing the same to a pair of the opposed side fins of the next adjacent bars.

12. A heater unit comprising a plurality-of elongated bars disposedin spaced generally parallel side by side relation one to the other with each' bar defining a passage for containing a heating fluid, each of said bars having a pair of fins projectingfrom each of the front,

rear and side faces thereof, said fins being substantially coextensive in length with said bars, means interconnecting said bars adjacent opposite ends thereof to per- I mit circulation of a fluid from one bar to another, means for closing the ends of said bars thereby providing a closed path for circulating fluid through the unit, means carried by said heater. unit for heating the fluid adapted to circulate through said bars including an electrical heating element, a thermostat connected to said heating element for activating said heating element in response to sensing a specified ambient air temperature, control means including temperature responsive means responsive to heater unit temperature for periodically activating and deactivating said heating element during the time said heating element is activated by said thermostat, said temperature responsive means being responsive to sensing a first predetermined heater unit temperature for activating said heating element and responsive to sensing a second predetermined heater unit temperature higher than said first predetermined temperature for deactivating said heating element whereby said heating element is operated cyclically during the timethe heating element is actir the front and side faces thereof,said fins being substan vatedby saidtheimostat, apair of elongated covers disposed between each next adjacent pair of said bars and respectively adjacent the front and rear sides thereof, means for connecting said covers to said next adjacent bars'whereby said pair of covers and next adjacent bars 5 define air ducts for circulating air heated by the fluid adapted to circulate through said passages, each of said coversbeing generally channel-shaped in cross section, and means carried by the legs of said channel-shaped covers for securing the same to a pair of the opposed side fins of the next adjacent bars, said closing means including a plurality of flexible elementsin the ends of each of the bars, means for compressing said flexible elements in a direction generally parallel to the axis of i said bar to laterally enlarge said elements into sealing engagement against the walls ofrsaid bar defining said passage thereby sealing the latter, a vent hole in one of said bars, a pressure relief valve for the closed circulation system including one of said sealing means compressed to a lesser extent than the other of said sealing means for sliding engagement along the associated bar thereby uncovering said vent hole.

13. A heater unit comprising a plurality of elongated bars disposed in spaced generally parallel side by side relation one to the other with each bar defining a passage for containing a heating fluid, means interconnecting said bars adjacent opposite ends thereof to permit circulation of fluid from one bar to another, each of said bars having a pair of fins projecting from each of tially coextensive in length with said bars, means carried by said heater unit for heating the fluid adapted to circulate through said bars, an elongated cover disposed between each next adjacent pair of bars adjacent are "2 ,561

a 1 the front sidesthereof, means for connecting said covers to said next adjacent bars whereby said covers and adjacent bars define air ductsfor circulating 'air heated by the fluid adapted .to circulate through said passages, means carried by said heater unit along the rear side of said bars and defining the rear surfaces for said air ducts, each of said covers being generally channelshaped in cross section and means carried by the legs of each channel-shaped cover for securing the same to a pair of opposed side fins of the next adjacent bars.

14. A heater unit according to claim .13 including means for closing the ends of said bars thereby providing a closedcirculation system, said heating means including an electrical heating element, a thermostat connected to said heating element for activating said heating element in response to the sensing of a specified ambient air temperature, and control means for periodically activating and deactivating said heating el- .ement during the time the heating element is activated by said thermostat. 4

15. A heater unit according to claim 14 wherein said control means includes temperature responsive means responsive to heater unit temperature for periodically activating and deactivating said heating element, said temperature responsive means being responsive to sensing a first predetermined heater unit temperature for activating said heating element and responsive to sensing a second predetermined heater unit temperature higher than said first predetermined temperature .for deactivating said heating element, whereby said heating element is operated cyclically during the time the heating element is activated by said thermostat. 

1. A heater unit comprising a plurality of elongated bars disposed in spaced generally parallel side by side relation one to the other with each bar defining a passage for containing a heating fluid, means interconnecting said bars adjacent opposite ends thereof to permit circulation of fluid from one bar to another, each of said bars having a pair of fins projecting from each of the front, rear and side faces thereof, said fins being substantially coextensive in length with said bars, means carried by said heater unit for heating the fluid adapted to circulate through said bars, a pair of elongated covers disposed between each next adjacent pair of bars and respectively adjacent the front and rear sides thereof, means for connecting said covers to said next adjacent bars whereby said pairs of covers and adjacent bars define air ducts for circulating air heated by the fluid adapted to circulate through said passages, each of said covers being generally channel-shaped in cross section, and means carried by the legs of each channel-shaped cover for securing the same to a pair of opposed side fins of the next adjacent bars.
 2. A heater unit according to claim 1 wherein the passages in the bars define a closed system for circulating fluid.
 3. A heater unit according to claim 2 wherein said heating means includes a heating element secured along one side of one of said bars.
 4. The heater unit according to claim 1 wherein said opposite side fins have beads projecting along their edges in a direction away from one another and defining grooves therewith, the legs of said covers having beads along their edges projecting toward one another, said legs being flexible to permit the beads carried thereby to snap past the beads carried by said fins for engagement within said grooves.
 5. A heater unit according to claim 1 including means for sealing the ends of the passages in said bars and including a flexible element in the ends of said passages, means for compressing said flexible element in a direction generally parallel to the axis of said bar to laterally enlarge said element into sealing engagement against the walls of said bar defining said passage to thereby seal the latter.
 6. A heater unit according to claim 1 including means for closing the ends of said bars thereby providing a closed circulation system, said heating means including an electrical heating element, a thermostat connected to said heating element for activating said heating element in response to the sensing of a specified ambient air temperature, and control means for periodically activating and deactivating said heating element during the time said heating element is activated by said thermostat.
 7. A heater unit according to claim 6 wherein said control means includes temperature responsive means responsive to heater unit temperature for activating said heating element in response to sensing a first predetermined temperature and for deactivating said heating element in response to sensing a second predetermined temperature higher than said first predetermined temperature.
 8. A heater unit according to claim 7 wherein said predetermined first and second temperatures constitute the surface temperatures of one of said bars adjacent said control means.
 9. A heater unit according to claim 1 including means carried thereby for circulating air through said ducts.
 10. A heater unit according to claim 1 including a heat exchange fluid in the passages of said bars and in said interconnecting means.
 11. A heater unit comprising a plurality of elongated bars disposed in spaced generally parallel side by side relation one to the other with each bar defining a passage for containing a heating fluid, each of said bars having a pair of fins projecting from each of the front, rear and side faces thereof, said fins being substantially coextensive in length with said bars, means interconnecting said bars adjacent opposite ends thereof to permit circulation of a fluid from one bar to another, means for closing the ends of said bars thereby providing a closed path for circulating fluid through the unit, means carried by said heater unit for heating the fluid adapted to circulate through said bars including an electrical heating element, a thermostat connected to said heating element for activating said heating element in response to sensing a specified ambient air temperature, control means including temperature responsive means responsive to heater unit temperature for periodically activating and deactivating said heating element during the time said heating element is activated by said thermostat, said temperature responsive means being responsive to sensing a first predetermined heater unit temperature for activating said heating element and responsive to sensing a second predetermined heater unit temperature higher than said first predetermined temperature for deactivating said heating element whereby said heating element is operated cyclically during the time the heating element is activated by said thermostat, a pair of elongated covers disposed between each next adjacent pair of said bars and respectively adjacent the front and rear sides thereof, means for connecting said covers to said next adjacent bars whereby said pair of covers and next adjacent bars define air ducts for circulating air heated by the fluid adapted to circulate through said passages, each of said covers being generally channel-shaped in cross section, and means carried by the legs of said channel-shaped covers for securing the same to a pair of the opposed side fins of the next adjacent bars.
 12. A heater unit comprising a plurality of elongated bars disposed in spaced generally parallel side by side relation one to the other with each bar defining a passage for containing a heating fluid, each of said bars having a pair of fins projecting from each of the front, rear and side faces thereof, said fins being substantially coextensive in length with said bars, means interconnecting said bars adjacent opposite ends thereof to permit circulation of a fluid from one bar to another, means for closing the ends of said bars thereby providing a closed path for circulating fluid through the unit, means carried by said heater unit for heating the fluid adapted to circulate through said bars including an electrical heating element, a thermostat connected to said heating element for activating said heating element in response to sensing a specified ambient air temperature, control means including temperature responsive means responsive to heater unit temperature for periodically activating and deactivating said heating element during the time said heating element is activated by said thermostat, said temperature responsive means being responsive to sensing a first predetermined heater unit temperature for activating said heating element and responsive to sensing a second predetermined heater unit temperature higher than said first predetermined temperature for deactivating said heating element whereby said heating element is operated cyclically during the time the heating element is activated by said thermostat, a pair of elongated covers disposed between each next adjacent pair of said bars and respectively adjacent the front and rear sides thereof, means for connecting said covers to said next adjacent bars whereby said pair of covers and next adjacent bars define air ducts for circulating air heated by the fluid adapted to circulate through said passages, each of said covers being generally channel-shaped in cross section, and means carried by the legs of said channel-shaped covers for securing the same to a pair of the opposed side fins of the next adjacent bars, said closing means including a plurality of flexible elements in the ends of each of the bars, means for compressing said flexible elements in a direction generally parallel to the axis of said bar to laterally enlarge said elements into sealing engagement against the walls of said bar defining said passage thereby sealing the latter, a vent hole in one of said bars, a pressure relief valve for the closed circulation system including one of said sealing means compressed to a lesser extent than the other of said sealing means for sliding engagement along the associated bar thereby uncovering said vent hole.
 13. A heater unit comprising a plurality of elongated bars disposed in spaced generally parallel side by side relation one to the other with each bar defining a passage for containing a heating fluid, means interconnecting said bars adjacent opposite ends thereof to permit circulation of fluid from one bar to another, each of said bars having a pair of fins projecting from each of the front and side faces thereof, said fins being substantially coextensive in length with said bars, means carried by said heater unit for heating the fluid adapted to circulate through said bars, an elongated cover disposed between each next adjacent pair of bars adjacent the front sides thereof, means for connecting said covers to said next adjacent bars whereby said covers and adjacent bars define air ducts for circulating air heated by the fluid adapted to circulate through said passages, means carried by said heater unit along the rear side of said bars and defining the rear surfaces for said air ducts, each of said covers being generally channel-shaped in cross section and means carried by the legs of each channel-shaped cover for securing the same to a pair of opposed side fins of the next adjacent bars.
 14. A heater unit according to claim 13 including means for closing the ends of said bars thereby providing a closed circulation system, said heating means including an electrical heating element, a thermostat connected to said heating element for activating said heating element in response to the sensing of a specified ambient air temperature, and control means for periodically activating and deactivating said heating element during the time the heating element is activated by said thermostat.
 15. A heater unit According to claim 14 wherein said control means includes temperature responsive means responsive to heater unit temperature for periodically activating and deactivating said heating element, said temperature responsive means being responsive to sensing a first predetermined heater unit temperature for activating said heating element and responsive to sensing a second predetermined heater unit temperature higher than said first predetermined temperature for deactivating said heating element, whereby said heating element is operated cyclically during the time the heating element is activated by said thermostat. 